We collected emission spectra using a spectrometer to verify the detected PL is due to SiV emission and perform HBT interferometry to confirm SPE statistics. Details on the setup are in the SI. The SiV spectrum in Figure REF a exhibits the characteristic zero-phonon line (ZPL) emission at 738 nm [1]}. Since we implanted on average 33.8 ions/spot, we can calculate the activation rate of the implanted Si to SiVs by counting the number of SiVs created. The implantation was performed with a pitch of 2 µm in both horizontal and vertical direction. The resulting array is shown in Figure REF b, with a zoomed in view of the area highlighted by the black box in Figure REF c and a linecut along the dashed line in Figure REF d. To calculate the SiV yield we define a grid over the array and at each point select a circular area with 2 µm diameter. We fit each area to a two-dimensional Gaussian to extract the amplitude of the PL. As the count rate for one SiV in the confocal microscope was found to be \(10.7 \pm 0.2\)  kcps, we use the bins \(0 \pm 5, 10 \pm 5, 20 \pm 5\) , etc. kcps to classify locations into containing 0, 1, 2, etc. SiV. Figure REF a shows the histogram acquired by this binning corresponding to the respective probability of finding a certain number of emitters at any location in the array. The histogram data was fitted to a Poisson distribution and we find that the average number of emitters per location is \(1.01 \pm 0.07\)  SiV, which translates to a conversion yield of \(2.98 + 0.21 / - 0.24 \%\)  from implanted Si to SiV.
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